fix: change identity handling for user & database (#50)

## Description

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relates to #1234

## Checklist

- [ ] Issue was linked above
- [ ] Code format was applied: `make fmt`
- [ ] Examples were added / adjusted (see `examples/` directory)
- [x] Docs are up-to-date: `make generate-docs` (will be checked by CI)
- [ ] Unit tests got implemented or updated
- [ ] Acceptance tests got implemented or updated (see e.g. [here](f5f99d1709/stackit/internal/services/dns/dns_acc_test.go))
- [x] Unit tests are passing: `make test` (will be checked by CI)
- [x] No linter issues: `make lint` (will be checked by CI)

Reviewed-on: #50
Reviewed-by: Marcel_Henselin <marcel.henselin@stackit.cloud>
Co-authored-by: Andre Harms <andre.harms@stackit.cloud>
Co-committed-by: Andre Harms <andre.harms@stackit.cloud>

stackit/internal/services/sqlserverflexbeta/user/mapper.go

@@ -165,7 +165,7 @@ func mapFieldsCreate(userResp *sqlserverflexbeta.CreateUserResponse, model *reso
 // toCreatePayload converts a resourceModel to an API CreateUserRequestPayload.
 func toCreatePayload(
 	model *resourceModel,
-	roles []sqlserverflexbeta.UserRole,
+	roles []string,
 ) (*sqlserverflexbeta.CreateUserRequestPayload, error) {
 	if model == nil {
 		return nil, fmt.Errorf("nil model")